This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | -1 |
| 2 | 4 |
| 3 | -13 |
| 4 | 40 |
| 5 | -121 |
| 6 | 364 |
| 7 | -1093 |
| 8 | 3280 |
| 9 | -9841 |
| 10 | 29524 |
| 11 | -88573 |
| 12 | 265720 |
| 13 | -797161 |
| 14 | 2391484 |
| 15 | -7174453 |
| 16 | 21523360 |
| 17 | -64570081 |
| 18 | 193710244 |
| 19 | -581130733 |
| 20 | 1743392200 |
| 21 | -5230176601 |
| 22 | 15690529804 |
| 23 | -47071589413 |
| 24 | 141214768240 |
| 25 | -423644304721 |
| 26 | 1270932914164 |